macOS External Drive Issues

Common external drive symptoms

• Drive not showing in Finder.
• Drive not appearing in Disk Utility.
• Drive connects and disconnects repeatedly.
• “The disk you attached was not readable by this computer.”
• Slow transfers or corrupted files.

Step 1 – Check Finder settings

Your drive may be connected but hidden.

1. Open Finder.
2. Go to Finder → Settings.
3. Under General, enable:
   • External disks
4. Under Sidebar, enable:
   • External disks

Step 2 – Check Disk Utility

If the drive appears here, macOS detects it but may not mount it.

1. Open Disk Utility.
2. Click View → Show All Devices.
3. Select the external drive.
4. If it’s grayed out, click Mount.
5. If errors appear, run First Aid.

Step 3 – Test cable, port, and adapter

Most external drive issues are caused by bad cables or adapters.

• Try a different USB‑C or USB‑A cable.
• Try another port on your Mac.
• Avoid USB hubs — connect directly.
• Try the drive on another computer.

Step 4 – Check power requirements

Some drives need more power than a single USB port can provide.

• Use a powered USB hub for large HDDs.
• Use the drive’s external power supply if it has one.
• Try connecting the drive while the Mac is plugged in.

Step 5 – Check drive format compatibility

macOS can read many formats but cannot write to some without extra software.

• NTFS (Windows) — read‑only on macOS.
• exFAT — fully compatible.
• FAT32 — compatible but limited.
• APFS / HFS+ — macOS formats.

If the drive is unreadable, you may need to reformat it.

Step 6 – Erase the drive (if needed)

Only do this if the drive is unreadable and you don’t need the data.

1. Open Disk Utility.
2. Select the external drive (top level).
3. Click Erase.
4. Choose:
   • exFAT for Mac + Windows
   • APFS for Mac only
5. Click Erase to confirm.

Step 7 – Run First Aid

Fixes file system errors that prevent mounting.

1. Open Disk Utility.
2. Select the external drive.
3. Click First Aid.

Step 8 – Test in Safe Mode

Safe Mode disables extensions that may block USB devices.

Apple silicon

1. Shut down.
2. Hold power until “Loading startup options”.
3. Select your disk → hold Shift → Continue in Safe Mode.

Intel Macs

1. Shut down.
2. Turn on and hold Shift.
3. Release at login screen.

Step 9 – Reset SMC (Intel Macs only)

SMC controls USB power and detection.

• MacBooks with T2 chip: Shut down → hold Control + Option + Shift for 7 seconds → keep holding and press power for 7 more seconds → release → wait → turn on.
• Older MacBooks: Shut down → hold Shift + Control + Option + power for 10 seconds → release → turn on.
• iMac/Mac mini: Shut down → unplug for 15 seconds → plug in → wait 5 seconds → turn on.

When it might be hardware

• Drive makes clicking or grinding noises.
• Drive disconnects when moved slightly.
• Drive not detected on any computer.
• USB ports on the Mac are loose or damaged.